Method of sintering of mineral sulphides

ABSTRACT

This invention relates to the sintering of sulphide minerals, e.g., lead sulphide, as a bed incorporating the same is conveyed substantially horizontally, e.g., in a sintering machine of the Dwight Lloyd-type, to a discharge position at which the sinter is delivered to sinter breaking means. According to the invention, the said bed is ignited at the bottom and then moves through three successive zones below a gas collecting enclosure. In the first of said zones, an updraught of air is passed through the bed so that the flame front moves upwardly therethrough substantially to its upper surface. In the second or intermediate zone, there is little, if any, flow of air through the bed while in the third zone, air is again passed upwardly through the bed thereby to cool the sinter. It is found that, during the interruption of the draught as the bed passes through the intermediate zone, the hot sinter tends to collapse to some extent so that it becomes more dense while still retaining its cellular structure. Also, there is an increased tendency for the molten metal to concentrate in the lower part of the bed. The strength of the sinter is increased by this method and may be broken into smaller pieces without the production of excessive fines and with reduced degradation during subsequent handling and transport. Also, it has been found practicable to include in the charge mixture, various materials, e.g., plant residues which have previously presented difficulties. According to a modification, gases from the said enclosure are withdrawn downwardly through the bed as it passes through the said second or intermediate zone.

United States Patent Cunningham [54] METHOD OF SINTERING OF MINERAL SULPHIDES [72] Inventor: Brian Charles Cunningham, Port Pirie,

South Australia, Australia The Broken Hill Associated Smelters Proprietary Limited, Melbourne, Victoria, Australia [22] Filed: Feb. 16, 1970 [21] Appl. No.: 11,436

[73] Assignee:

Primary Examiner-Allen B. Curtis Attomey-Pierce, Scheffler & Parker Mar. 14, 1972 e.g., lead sulphide, as a bed incorporating the same is conveyed substantially horizontally, e.g., in a sintering machine of the Dwight Lloyd-type, to a discharge position at which the sinter is delivered to sinter breaking means.

According to the invention, the said bed is ignited at the bottom and then moves through three successive zones below a gas collecting enclosure.

ln the first of said zones, an updraught of air is passed through the bed so that the flame front moves upwardly therethrough substantially to its upper surface.

In the second or intermediate zone, there is little, if any, flow of air through the bed while in the third zone, air is again passed upwardly through the bed thereby to cool the sinter.

It is found that, during the interruption of the draught as the bed passes through the intermediate zone, the hot sinter tends to collapse to some extent so that it becomes more dense while still retaining its cellular structure. Also, there is an increased tendency for the molten metal to concentrate in the lower part of the bed.

The strength of the sinter is increased by this method and may be broken into smaller pieces without the production of excessive fines and with reduced degradation during subsequent handling and transport. Also, it has been found practicable to include in the charge mixture, various materials, e.g., plant residues which have previously presented difficulties.

According to a modification, gases from the said enclosure are withdrawn downwardly through the bed as it passes through 57 ABSTRACT the said second or intermediate zone.

This invention relates to the sintering of sulphide minerals, 8Claims,3l)rawing Figures A e c D j l 29 Z 28 n 34 3O 50 l 1 a, 18 20 a m L4 "in 18 26 f l A 26- r e l k l 22a- 22b He 222 7.2; 22 22h Ht 16 l k 10 L W g 56 METHOD OF SINTERING OF MINERAL SULPHIDES This invention relates to the updraught sintering of mineral sulphides, especially lead and zinc sulphide ores and concentrates, though the invention is not limited thereto.

It is now well known to subject a horizontally moving bed, comprising mineral sulphides, to an updraught sintering operation though for many years previously, downdraught sintering was carried out on similar machines and this is still the more general practice.

As compared with downdraught sintering, the updraught procedure provides important advantages in that it facilitates the collection of SO gas of higher tenor for the production of sulphuric acid, and also substantially reduces lead fall, i.e., the deposition of metallic lead through the bottom of the bed.

In updraught sintering as presently practised, a bed of suita ble charge material and required depth is continuously formed on a horizontally movable grate or the like. This bed is continuously ignited at the bottom and air is continuously blown upwardly through the bed until it approaches the opposite end of the machine where it passes to a breaker by which it is reduced to lumps of a suitable maximum size. The broken material is then screened, the oversize material being used as feed material for the blast furnaces while the undersize material is returned to the sinter bed makeup plant.

The ignition of the sinter bed at the bottom is usually affected by forming a thin layer of sulphide-bearing or other combustible material on the travelling grate or strand, and by igniting this layer while air is passed downwardly therethrough, after which the charge bed is formed on top of this burning layer and air is passed upwardly therethrough.

The general object of this invention is to provide improvements in the updraught sintering of mineral sulphides whereby the quality of the sinter is improved in a manner which facilitates its subsequent handling and smelting in a blast furnace or the like.

Accordingly, the invention provides the method of sintering mineral sulphides comprising progressively igniting, at the bottom thereof, a substantially horizontally moving bed of sulphide bearing charge material, passing air upwardly through the bed during an initial zone of its subsequent movement, thereby to effect a required degree of sulphur elimination, then discontinuing or reducing the updraught as the bed passes through a second or intermediate zone of its movement, and then again passing air upwardly through the bed during a further zone of its movement.

More particularly, the initial updraught zone is preferably of a length such that, shortly before the bed enters the said intermediate zone, the upwardly moving flame front breaks through to the surface of the bed thereby ensuring the desired degree of sulphur elimination.

During the interruption or reduction of the updraught, as the bed passes through the said intermediate zone, the hot sinter tends to collapse to some extent so that it becomes more dense while still retaining its cellular structure. Also, it is found that there is an increased tendency for the molten metal produced during the preceding updraught stage to concentrate in the lower part of the bed.

Thus, due both to its increased density and the increased concentration of metal in the lower part of the sinter bed, the strength of the sinter is increased so that during subsequent handling and transport, it is less subject to degradation, while also the quality of the oversize fraction delivered to the blast furnace is improved both because it contains a greater proportion of metallic lead and because of its improved strength and structure. Conversely as the undersize fraction which is returned to the sinter plant contains less lead, it passes more smoothly through the secondary crusher in the sinter returns circuit.

According to a modification, some or all of the gases discharged upwardly through the bed in the initial zone or in the final zone, or both, are returned downwardly through the bed as it moves through the intermediate zone thereby tending further to increase the density of the bed and also to increase sulphur recovery and or the S tenor of the gas.

- It is known that sinter lump size and sinter size range are important factors in achieving efficient blast furnace performance and in particular, it appears that optimum bed permeability is obtained when the lumps are substantially uniform in size. Also, our investigations have shown that, in the case of sinter produced from lead sulphide ores and concentrates, lump sizes of the order of 3 inches to 1 inch are generally desirable.

However, in the past, it has been the general practice to break the sinter into lumps of a maximum size of the order of about 5 inches with the simultaneous production of a considerable proportion of smaller lumps as well as fines.

Consequently, the oversize fraction supplied to the blast furnaces has a considerable size range varying from relatively large lumps to small pieces as well as a substantial proportion of fines produced chiefly by degradation, particularly of the larger lumps, during transport and handling. This degradation was considerable both because of the lower strength of the sinter and because lumps larger than an experimentally ascertainable terminal size, break very readily into smaller pieces when dropped.

However, due to the low strength of the sinter as previously produced, it was not practicable to break the sinter initially into lumps of a maximum size approaching the terminal size because this would have resulted in the simultaneous production of an excessive proportion of fines.

Due, however, to the increased strength of sinter produced according to the present invention, it has been found practicable to break it into smaller lumps without producing excessive fines, while also degradation during handling and transport is considerably reduced.

Also, although a variable quantity of the undersize fraction is required for use as return sinter, it has been found that with the improved sinter produced according to the present invention, practically all of the fragments, below about two inches, are generally required for this purpose. Consequently, the oversize fraction supplied to the blast furnaces is fairly uniform in size and contains minimal undersize material, as due to the increased strength of the sinter and the smaller maximum size, it does not suffer significant degradation when later subjected to normal handling before delivery into the furnace.

Improved blast furnace operation and treatment rates are therefore obtainable while also, due to its lower content of metallic lead, the returns sinter is more readily handled in the sinter returns circuit.

Also, due to the improved quality of the sinter produced according to the method of this invention, it has been found practicable to include in the charge bed, various materials, e.g., plant residues, the incorporation of which previously presented difficulties because they were detrimental to the operation of the sinter plant or the blast furnace or both. Thus, it is possible to sinter a plant feed with a wider range of chemical and or physical properties.

In order that the invention may be more fully understood, representative applications thereof are further described below with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic view in sectional side elevation of an updraught sintering machine in accordance with the invention,

FIG. 2 is a view in sectional end elevation to a larger scale taken on the line 2-2 of FIG. 1, and

FIG. 3 is a view similar to FIG. 1 and shows a modification of the invention.

The machine shown in FIGS. 1 and 2 comprises upper and lower tracks for pallets 10 which are raised from the lower track to the upper track by sprockets (not shown) arranged at the feed end of the machine, and which are transferred from the upper to the lower tracks by sprockets at the discharge end of the machine.

The pallets while moving along the upper track form a continuous horizontally movable grate and a thin ignition layer ll of charge material comprising sulphide ore, e.g., lead sulphide ore, is deposited thereon from a hopper 12 arranged adjacent to the feed end of the machine.

As this ignition layer is moved forwardly by the pallets from the hopper 12, it passes below an ignition stove 14 by which it is ignited, while subjected to a downdraught by means of a suction windbox 16 arranged below the grate.

Immediately after the burning layer 1 1 passes beyond the ignition stove, a charge bed 18 of required depth is formed thereon by means of a charge hopper 20 disposed immediately in advance of the first of a series of nine pressure windboxes 22a, 22b-22i disposed below the grate and extending to the opposite end of the machine.

The lower end of each windbox is connected by a branch pipe to a header pipe 36 which is provided at intervals with shutoff valves 38 which subdivide the header pipe into sections and enable corresponding groups of the windboxes to be isolated. A fan 40, 42, 44 or 46 is provided for supplying air under pressure to each section of the header pipe and each fan is desirably automatically controlled so as to maintain a predetermined discharge rate irrespective of variations in the permeability of the charge bed.

Thus, immediately after the charge bed 18 is formed, the direction of the draught is reversed so that it passes upwardly through the burning ignition layer 11 and the charge bed 18 which latter is thus ignited at its lower surface whereby combustion then proceeds upwardly therethrough as the bed moves towards the discharge end of the machine.

The space above the bed is enclosed in a gas collection hood 24 which is substantially sealed from the external atmosphere and which may be supported by spaced arch trusses 26. Preferably, the gas pressure maintained within the hood space is approximately equal to but preferably is slightly lower than the external atmospheric pressure to prevent the escape of gases therefrom and also to minimize inward leakage of air thereto.

Gas offtake pipes 28 and 30 are connected to the opposite end portions of the hood, the pipe 28 near the feed end serving to supply gas rich in SO to a sulphuric acid plant, while the pipe 30 conveys waste gases to a baghouse filter plant. The pipes 28 and 30 are connected by a pipe 32 incorporating a valve 34 whereby if required, some of the acid gas may be mixed and discharged with the waste gases or vice versa.

The illustrated sinter machine is one which was constructed and previously used for continuous updraught operation, though normally only the first six windboxes were used. Thus, the fan 46 was not normally operated and the valve 38 adjacent thereto was closed while the other valves 38 were open.

in the illustrated application of the present invention, however, air is supplied only to windboxes 22a, 22b, 22 and 22f and so that neither the fan 46 nor the fan 42 is operated and all three valves 38 are closed.

The sinter bed is thus divided into four successive zones designated A, B, C and D of which A is the initial updraught zone above the first and second windboxes, B is an intermediate zone in which there is substantially no draught. C is a second updraught zone, and D is an extension zone which enables the windbox groupings to be varied but which is not utilized in the illustrated application of the invention.

Consequently, as the charge bed 18 passes above the first and second windboxes (zone A), the flame front progresses upwardly through it and reaches the upper surface of the bed shortly in advance of zone B. As the bed passes through zone B, very little, if any, air passes upwardly through it, though generally there is a small updraught due to leakage from the adjacent second and fifth windboxes 22b and 22e respectively. At this time, therefore, the sinter bed collapses to some extent as previously described.

As the bed passes over the fifth and sixth windboxes (zone C), it is again subjected to an Updraught from the fan 44 which serves to cool the sinter, while in passing over the final three windboxes (zone D) to the breaker (not shown), there is again substantially no air passing through the bed.

The present invention incidentally, provides some economy in power consumption as fan 42 is not operated.

it is to be understood that different windbox groupings may be used in carrying out the invention though the described grouping has been found to provide good results.

Comparisons of sinter obtained by the discontinuous updraught method of the present invention from a charge bed comprising lead sulphide mined at Broken Hill, Australia, with sinter produced from similar material by the prior continuous updraught treatment, have shown the following differences:

I. Sinter Hardness The following representative values of Drop Shatter index were obtained:

a. Continuous Updraught process, 12.5

b. Discontinuous Updraught process 5.3

2. Lead Content and Distribution a. As compared with sinter produced by the continuous process, sinter produced by the discontinuous process of the present invention contained about 1.8 percent less lead in the upper surface layer of the sinter and an increase of about 6.6 percent in the bottom layer.

b. Physical examination of the two sinter cakes showed that sinter produced by the discontinuous process, displayed a band of metallic lead/sinter matrix immediately above the bottom of the cake whereas no such band was apparent in the cake produced by the continuous process.

Also, in operating the discontinuous process, the proportion of crude metallics in the crushed return sinter was markedly less, while also it was found practicable to incorporate in the sinter feed substantially larger proportions of low-grade leadcontaining materials such as oxidized ore, middlings, slimes and zinc plant residues, without materially affecting sinter quality or blast furnace operation or efficiency, thus facilitating the recovery of values from such low grade materials.

According to one modification which is illustrated in FIG. 3, the lower ends of windboxes 22c and 22d are connected to the intake of a suction fan 48 which withdraws gas downwardly through the sinter bed from the hood space. in such circumstances, the acid gas offtake pipe 28 may be partly closed by valve 29 so that some of this acid gas is recirculated downwardly through the sinter bed, and then directed by pipe 49 into the first and second windboxes, before it is delivered through pipe 28 to the acid plant, though alternatively the gases withdrawn by the suction fan could be delivered direct to the acid gas offtake pipe 28. It will be apparent that this downdraught in zone B tends further to densify the hot sinter, while also some improvement in $0 tenor is obtainable in this way.

i claim:

1. The method of sintering mineral sulphides comprising progressively igniting, at the bottom thereof, a substantially horizontally moving bed of sulphide bearing charge material, passing air upwardly through the bed during an initial zone of its subsequent movement thereby to effect a required degree of sulphur elimination, then discontinuing or substantially reducing the updraught as the bed passes through a second or intermediate zone of its movement, whereby little, if any, air passes upwardly through the bed in said second or inter mediate zone, and then again passing air upwardly through the bed during a further zone of its movement.

2. The method of sintering mineral sulphides comprising progressively forming a charge bed, comprising said mineral sulphides, on a continuously and substantially horizontally moving porous surface, progressively igniting said charge bed at the bottom thereof and then moving the bed below a gas collecting enclosure through three successive zones comprising, an initial zone in which air is passed upwardly at a suitable velocity through the bed thereby to cause the flame front to move upwardly through the bed and substantially to the surface thereof, a second or intermediate zone in which the updraught is discontinued or substantially reduced so that little, if any, air passes upwardly through the bed, and a third zone in which air is again passed upwardly through the bed at a suitable velocity thereby to cool the sinter, subsequently progressively breaking the cooled sinter into pieces, and continuously withdrawing gases from said gas collecting enclosure.

3. The method according to claim 2 comprising continu' ously forming a relatively thin ignition layer of combustible material on said porous surface before said charge bed is formed thereon, progressively igniting said ignition layer at its upper surface while passing air downwardly therethrough, and then forming said charge bed on the top of the burning ignition layer.

4. The method according to claim 2, wherein gases from said gas-collecting enclosure are withdrawn downwardly through the sinter bed as it passes through the said second or intermediate zone of its movement.

5. The method according to claim 4, wherein the gases withdrawn downwardly through the sinter bed, as it passes through said second or intermediate zone, are returned upwardly through the bed in said initial zone.

6. The method according to claim 2, including continuously x0. 3, 9, 4 Dated March 1 1972 Izzventor BRIAN CHARLES CUNNINGHAM I: is certified the: error appears in the ebove-idezzif1ed pazeflr.

and :aa z' said Le;ters Pazentere hereby corrected as shombelow:

I Cieim {lines 1' end a d charge bed" shoe id w cooled sincer" i V g, 1-1.. I I

-'sigh ej-Qha"ere-211wnus zzndea 'b'f Au g pst 1972.

.EDWA'R'D 'M'JFLE'TGH R; 1. .4 I *fROBER'T -G QITSCHALK Atiie s ting Offijc'e r' Commissioner. of Patents 1 I. ne 

2. The method of sintering mineral sulphides comprising progressively forming a charge bed, comprising said mineral sulphides, on a continuously and substantially horizontally moving porous surface, progressively igniting said charge bed at the bottom thereof and then moving the bed below a gas collecting enclosure through three successive zones comprising, an initial zone in which air is passed upwardly at a suitable velocity through the bed thereby to cause the flame front to move upwardly through the bed and substantially to the surface thereof, a second or intermediate zone in which the updraught is discontinued or substantially reduced so that little, if any, air passes upwardly through the bed, and a third zone in which air is again passed upwardly through the bed at a suitable velocity thereby to cool the sinter, subsequently progressively breaking the cooled sinter into pieces, and continuously withdrawing gases from said gas collecting enclosure.
 3. The method according to claim 2 comprising continuously forming a relatively thin ignition layer of combustible material on said porous surface before said charge bed is formed thereon, progressively igniting said ignition layer at its upper surface while passing air downwardly therethrough, and then forming said charge bed on the top of the burning ignition layer.
 4. The method according to claim 2, wherein gases from said gas-collecting enclosure are withdrawn downwardly through the sinter bed as it passes through the said second or intermediate zone of its movement.
 5. The method according to claim 4, wherein the gases withdrawn downwardly through the sinter bed, as it passes through said second or intermediate zone, are returned upwardly through the bed in said initial zone.
 6. The method according to claim 2, including continuously withdrawing gases from that end portion of said gas-collecting enclosure which extends above said initial zone of movement of the charge bed, directing such gases, containing a relatively high proportion of SO2, to a sulphuric plant, and continuously withdrawing gases, low in SO2, from the opposite end portion of said gas collecting enclosure.
 7. The method according to claim 2 wherein said charge bed is broken into pieces of maximum size of about 3 inches.
 8. The method according to claim 2 wherein the length of said second or intermediate zones approximates the length of said initial zone. 